1. Field of the Invention
The present invention relates to a numerical control apparatus having a three-dimensional graphic display function and, more particularly, to a numerical control apparatus having a three-dimensional display function for providing three-dimensional simulation of the processing of a form defined in a three-dimensional space.
2. Description of the Prior Art
In the numerical control apparatus (hereinafter referred to as NC apparatus) having a graphic display function, a method has been put into practical use in which processing is three-dimensionally simulated in a three-dimensional space using the forms of a workpiece and a tool defined in a three-dimensional space. Specifically, the method described below are for defining the forms of a workpiece and a tool in a three-dimensional space as follows.
First, there is a method wherein a plane including two of three-dimensional coordinate axes is divided into lattice points as shown in FIG. 1A; the height data of a workpiece and a tool are applied to each lattice point as shown in FIG. 1B; and the display of the forms of the workpiece and the tool is constructed as shown in FIG. 1C based on the data (refer to Japanese Patent Laid-open No. 189011/1985).
In this method, the data of the forms of a workpiece and a tool are handled on the assumption that there is no discontinuity in the forms of the workpiece and the tool in the direction of the axis perpendicular to the plane divided into lattice points. Therefore, for example, even if a workpiece is divided into 256 steps in the direction of the axis perpendicular to the plane divided into lattice points, these steps can be represented by a minimum of 8 bits and, therefore, there is an advantage that the form data of a workpiece and a tool can be stored using a small memory capacity.
Next, there is a method wherein a three-dimensional space as a whole is divided into lattice points as shown in FIG. 2A; the form data of a workpiece and a tool are represented using binary data for each lattice point as shown in FIG. 2B; and the display of the forms of the workpiece and the tool is constructed as shown in FIG. 2C. This method is advantageous in that it allows display of any kind of processing because every lattice point can have arbitrary binary data.
Although the above-described conventional three-dimensional graphic methods have the noted advantages, they also suffer the following problems. In the former method, since it is assumed that there is no discontinuity in the workpiece and the tool, a problem exists in that the display can not be appropriate for processing wherein the center axis of the tool is included in the plane on which the lattice points are defined (multi-plane processing). In the latter method, if a workpiece is divided into 256 steps in the direction of one of the axes, for example, at least 256 bits are required to represent these steps. In other words, there is a problem in that a large amount of memory capacity is required.
In either method, since the entire form data is handled without adding weight, portions which have gone though a roughing process and portions under a finishing process in progress are represented in the same level of accuracy. In other words, in order to improve the accuracy of display in a certain portion, it is necessary to increase the number of lattice points accordingly, resulting in a problem in that the memory capacity must be increased.